1. Field of the Invention
The present invention relates to a cleaning device for removing toner particles adhered to or remaining on a cleaning target which is directly or indirectly heated by a heater, and a fixing device and an image forming apparatus using the cleaning device.
2. Description of the Background
Electrophotographic image forming apparatuses, such as copiers, printers, facsimile machines, and multifunctional peripherals, equipped with a transfixing device which simultaneously performs a transfer process and a fixing process, are known. For example, Unexamined Japanese Patent Application Publication No. (hereinafter “JP-A”) 2004-145260 discloses an image forming apparatus equipped with such a transfixing device.
Such an image forming apparatus equipped with a transfixing device has an advantage over an apparatus that performs transfer and fixing processes separately because the resultant image quality hardly deteriorates even with rough-surfaced recording media.
In particular, when a recording medium having a rough surface is used for an image forming apparatus which performs transfer and fixing processes separately, an intermediate transfer member such as an intermediate transfer belt cannot follow the surface roughness of the recording medium. As a result, a microgap is formed between the intermediate transfer member and the recording medium. Since abnormal discharge tends to occur in the microgap, a toner image on the intermediate transfer member may be abnormally transferred onto the recording medium, resulting in production of an uneven image.
On the other hand, in an image forming apparatus equipped with a transfixing device, a toner image is heated when transferred. Therefore, the toner image is softened and melted, and becomes a toner block having viscoelasticity. The toner block having viscoelasticity may be normally transferred onto the recording medium having a rough surface even if a microgap is formed between the intermediate transfer member and the recording medium. Accordingly, a high quality image can be produced.
Furthermore, the intermediate transfer member can be set to a relatively lower temperature in the image forming apparatus equipped with a transfixing device compared to those that separately perform transfer and fixing processes, because a toner image can be heated for a longer time therein. Therefore, thermal energy consumption can be reduced.
The following patent documents have disclosed fixing devices employing a cleaning technique for removing toner particles, paper powders, etc., remaining on a fixing roller. In particular, the following fixing devices are used for an image forming apparatus which separately perform transfer and fixing processes.
For example, JP-A 08-202195 discloses a fixing device including a cleaning roller (serving as a cleaning member) to remove toner particles remaining on a fixing roller (serving as a cleaning target) by contacting the fixing roller, and a blade (serving as a blade member) to remove toner particles adhered to the cleaning roller by contacting the cleaning roller. The surface of the blade is coated with a fluorocarbon resin so that the blade and the cleaning roller do not lock.
JP-A 11-194646 discloses a fixing cleaning device including a cleaning roller and a blade, in which a leading edge of the blade is plated with nickel containing TEFLON® so that the blade and the cleaning roller do not lock.
Japanese Patent No. 3318136 discloses a fixing device including a cleaning roller, the surface of which is coated with a mixture of polyimide and tetrafluoroethylene, and blade, so that durability of the cleaning roller improves.
JP-A 2005-148322 discloses a fixing member including a release layer which has a specific water contact angle, and a fixing device using the fixing member.
When the above-described cleaning devices are applied to a transfixing device, the cleaning member and the blade member in some cases do lock. This is because an overwhelmingly greater number of toner particles, which are heated, enter the cleaning member in the transfixing device compared to in the typical fixing device. Consequently, when a paper jam occurs in an image forming apparatus employing the transfixing device, an extremely large number of toner particles which are neither transferred nor fixed may remain on the fixing member (i.e., a cleaning target). In addition, undesired toner particles adhered to non-image portions also remain on the fixing member, and cause background fouling in the resultant image.
Even if toner-releasing ability of a surface (i.e., a portion which contacts the cleaning member) of the blade member is enhanced, toner particles accumulated on the blade member are repeatedly heated and cooled, resulting in formation of a toner block. The toner block prevents the cleaning member from rotating, thereby overloading a driving source (i.e., a motor) which drives the cleaning member to rotate.
If the toner block is broken, fragments thereof may not be sufficiently removed from the cleaning member, and may strongly adhere to or remain on part of the cleaning member. As a result, the cleaning target and the cleaning member may be in uneven contact with each other or the leading edge of the blade member may be damaged.
To solve the above-described problems, one proposed approach involves heating the cleaning member and blade member using a heater to melt a toner block. However, this technique may waste time and electric power for melting the toner block, and there is also the cost of providing the heater.
Alternatively, another proposed approach involves enhancing toner-releasing ability of the surface of the cleaning member, so that strongly-adhered toner particles are easily separated therefrom. However, this technique has a drawback in that the ability of the cleaning blade to remove remaining toner particles from the cleaning target, which is the original function of the cleaning blade, may deteriorate as a result.
The above-described problems are especially prominent in a cleaning device provided for the transfixing device and also in a cleaning device provided for the typical fixing device, particularly when an extremely large number of heated toner particles enter the fixing member or the fixing member is repeatedly cleaned for an extended period of time.
On the other hand, JP-A 2005-128417 discloses an image forming apparatus employing a transfixing device including a pressing member (i.e., a pressing roller) to remove toner particles remaining on a fixing member (i.e., a transfixing belt) and a blade member (i.e., a cleaning blade) in contact with the pressing member.
When an image having background fouling, in which the background portion of an image is soiled with toner particles, is continuously produced by the above-described image forming apparatus, that is an indication that the cleaning blade does not sufficiently clean the fixing member and the pressing member, for the reason described below.
Originally, toner particles used for an electrophotographic image forming apparatus should be sufficiently charged so as to form a toner image on image bearing members such as a photoconductor and an intermediate transfer member. If insufficiently-charged toner particles (i.e., weakly-charged and reversely-charged toner particles) are produced in a developing process, these toner particles may adhere to background portions on the image bearing members, causing background fouling. The background fouling may occur at any portion (i.e., an effective region for bearing an image) on the image bearing members, regardless of the size of a recording medium on which an image is to be formed.
Even if an image is to be formed on an A4-size recording medium, the background fouling may occur beyond the image region having a size of A4 on the image bearing member. Background fouling occurring within the A4-size image region may be transfixed onto the recording medium together with the original image. By contrast, background fouling occurring beyond the A4-size image region may not be transfixed on the recording medium, and may be accumulated on the cleaning blade.
Consequently, the cleaning blade cannot scrape off melted toner particles adhered to the fixing member and the pressing member. More specifically, the melted toner particles pass under the leading edge of the cleaning blade, resulting in contamination of the recording medium. The above-described phenomenon notably occurs particularly when an image having background fouling is continuously produced using the transfixing device.
Moreover, when an image is to be formed on a larger recording medium (e.g., an A3-size recording medium) after the above-described continuous production of the image having background fouling, the background portion of which is included within the A3-size region, toner particles accumulated on the cleaning blade tend to adhere to the resultant image, even if cleaning is normally performed in the continuous production of the image.
Furthermore, toner particles accumulated on the cleaning blade while the apparatus is not operated tend to strongly adhere thereon, resulting in lock-up of a rotation member in contact with the cleaning blade when the apparatus is started to operate.
The above-described phenomenon typically occurs in an image forming apparatus equipped with a transfixing device, not in an image forming apparatus that separately performs transfer and fixing processes. This is because, in the image forming apparatus that separately performs transfer and fixing processes, only a recording medium onto which a toner image is transferred from image bearing members (such as a photoconductor or an intermediate transfer member) enters a fixing device. Therefore, background fouling occurring in a region larger than the size of the recording medium never directly enters the fixing device.
In yet another approach, JP-A 2001-235987 discloses an image forming apparatus which separately performs transfer and fixing processes, in which a cleaning blade and a cleaning brush are provided so as to remove toner particles remaining on a photoconductor (i.e., an image bearing member) instead of a fixing member. The cleaning brush is provided on an upstream side from the cleaning blade relative to the direction of rotation of the photoconductor.
However, toner particles remaining on a photoconductor are in different state from melted or half-solidified toner particles remaining on a fixing member. Therefore, the cleaning techniques disclosed therein cannot be applied to a transfixing device.